Electroless plating was employed for making copper (Cu)-high density polyethylene (HDPE) core-shell particles for following coating deposition by flame spraying. Our previous works already reported large-scale fabrication of HDPE/Cu composite coatings against corrosion, biofouling and ageing for marine applications. In this work, we further investigated tribological behaviours of the HDPE and the HDPE/Cu composite coatings. The structure of the composite coatings was designed via controlling the thickness of the copper shell coated on the composite powder. The result shows that the addition of copper slightly decreased the anti-wear property of the composite coating. The tribology mechanisms of the composite coating and the HDPE coating were discussed.

There have been increasing demands for adequate gas sensors to monitor O 3 , a respiratory irritant gas associated with a spectrum of adverse health events. Here we report film construction by liquid flame spray route and characterization of nanostructured WO 3 -reduced graphene oxide (rGO) composites and their gas-sensing activities to O 3 . The starting feedstock was prepared from WCl 6 and rGO for pyrolysis synthesis by flame spray. Nanosized WO 3 grains exhibited oriented nucleation on rGO flakes and rGO retained intact nano-structural features after the spraying. Constrained grain growth of WO 3 was realized in the rGO-containing films with 60-70 nm size as compared to ~220 nm in the pure WO 3 film. The WO 3 -rGO film sensors showed quicker response to O 3 and faster recovery than the rGO-free WO 3 film sensors. Addition of rGO in 1.0wt.% or 3.0wt.% in the films caused significantly reduced effective working temperature of the film sensors from ~250°C to ~150°C. These results might shed some light on liquid flame spray fabrication of novel functional nanocomposites for gas-sensing applications.

Development of TBCs allowing higher combustion temperatures in gas turbines is of high commercial interest since it results in higher fuel efficiency and lower emissions. It is well known that TBCs produced by suspension plasma spraying (SPS) have lower thermal conductivity as compared to conventional systems due to their very fine porous microstructure. Moreover, columnar structured SPS TBCs are significantly cheaper to produce as compared to the conventionally used electron beam – physical vapour deposition (EB-PVD). However, SPS TBCs have not yet been commercialised due to low reliability and life expectancy of the coatings. Lifetime of a TBC system is significantly dependent on topcoat-bondcoat interface topography. The objective of this work was to study the effect of topcoat-bondcoat interface in SPS TBCs by changing bondcoat spray parameters and bondcoat surface heat treatment. High velocity air fuel (HVAF) spraying was used for bondcoat deposition while axial-SPS was used for topcoat deposition. Same topcoat spray parameters were used for all samples. Lifetime was examined by thermal cyclic fatigue and thermal shock testing. The influence of surface roughness on lifetime has been discussed. The results show that HVAF could be a suitable process for bondcoat deposition to achieve long lifetime SPS TBCs.

Polyimide-copper layers consisting of individual capsule-like splats were one-step fabricated by solution precursor flame spray through controlling the reaction between dianhydride and diamine dissolved in copper nanoparticles containing dimethylformamide solvent. The polyimide splat exhibited hollow structure with an inner pore of 10-15 µm and a tiny hole of 1-5 µm on its top surface. Transversal cut by focused ion beam milling of the individual splats and scanning electron microscopy characterization further revealed unique dispersion of the copper nanoparticles inside the polyimide shell. After 1000 h exposure to the testing synthetic seawater, continuous release of copper from the coatings containing up to 30wt.%Cu kept remarkable. Antifouling performances of the constructed layers were assessed by examining colonization behaviors of typical bacteria Bacillus sp. and marine algae Phaeodactylum tricornutum and Chlorella on their surfaces. Distribution of the inorganic nanoparticles endows the polyimide coatings with special capsule structure and exciting hydrophobicity and antifouling performances. The liquid flame spray route and the encapsulated structure of the polyimide-Cu coatings would open a new window for designing and constructing environment-friendly marine antifouling layers for long-term applications.

An alumina-silicon dioxide composite coating was fabricated by cold spraying on AZ31 magnesium alloy. The microstructure, mechanical properties (microhardness, bonding strength and tribological behaviour) and anticorrosion property of the coating as a function of the ceramic volume were investigated. The results show that the composite coating presents higher bonding strength and microhardness. Addition of silicon dioxide significantly enhances the anti-wear and anti-corrosion performances of AZ31 magnesium alloy.

Development of thermal barrier coatings (TBCs) manufactured by suspension plasma spraying (SPS) is of high commercial interest as SPS has been shown capable to produce columnar microstructures similar to the conventionally used electron beam – physical vapour deposition (EB-PVD) process. Moreover, SPS is a significantly cheaper process and can also produce more porous coatings than EB-PVD. However, lifetime of SPS coatings needs to be improved further for them to be applicable in commercial applications. The bondcoat microstructure as well as topcoat-bondcoat interface topography affect the TBC lifetime significantly. The objective of this work was to investigate the feasibility of different bondcoat deposition process for SPS TBCs. In this work, a NiCoCrAlY bondcoat deposited by high velocity air fuel (HVAF) was compared to commercial NiCoCrAlY and PtAl bondcoats. All bondcoat variations were prepared with and without grit blasting the bondcoat surface. SPS was used to deposit the topcoats on all samples using the same spray parameters. Lifetime of these samples was examined by thermal cyclic fatigue and thermal shock testing. The effect of bondcoat deposition process and interface topography on lifetime in each case has been discussed. The results show that HVAF could be a suitable process for bondcoat deposition in SPS TBCs.

This study evaluates the effect of Ru and Ce on the oxidation behavior of NiCoCrAl coatings deposited by HVOF spraying. Isothermal oxidation tests were conducted at 900, 1000, and 1100 °C. Test samples were also cycled between 100 °C and 1100 °C, with a dwell time of 1 h at 1100 °C. In both cases, coatings with Ru had a lower oxidation rate than those with Ce additions. β-depletion due to interdiffusion was also found to be lower when Ru was present. To help explain the findings, simulation results are presented and discussed along with observations on the influence of oxidation time on microstructure evolution.

This paper describes the fabrication of corrosion-resistant HDPE coatings with antifouling properties achieved through the dispersion of Cu particles. The main feedstock powder was prepared by coating HDPE particles with a 1 μm thick Cu shell via electroless plating. The coated particles were flame sprayed as a topcoat over HDPE and Cu layers that had been deposited on mild steel substrates. SEM, EDS, and XRD analysis was used to examine the coatings and feedstock powders. After neutral salt spray testing for 14 days, the HDPE-Cu coatings were found to be relatively intact. Coating samples of various types were also immersed in bacteria-containing artificial seawater for three days. Field-emission SEM showed that the attachment of Bacillus sp., which successfully colonized on HDPE surfaces, was significantly constrained on pure copper and HDPE-Cu composite coatings. Some of the proposed theories on how Cu ions inhibit the formation of biofilms are discussed.

This study evaluates a method for producing Gd 2 Zr 2 O 7 /SrZrO 3 , a ceramic-matrix composite considered for use as a thermal barrier coating. GdZrO/SrZrO powders are synthesized by co-precipitation, then cold pressed and sintered to form the bulk composite material. Phase stability of the powder and bulk material is assessed by X-ray diffraction and several bulk material properties are determined, including microhardness, Young’s modulus, fracture toughness, thermal expansion coefficient, heat capacity, thermal diffusivity, and thermal conductivity. The results are presented and discussed.

In this work, Yb 2 Si 2 O 7 powder was synthesized from Yb 2 O 3 and SiO 2 powders and applied to aluminum substrates by atmospheric plasma spraying. Phase composition and microstructure were examined and density, porosity, and hardness were assessed. Thermal stability was evaluated by thermogravimetry and differential thermal analysis and thermal conductivity was measured. The as-sprayed coating was mainly composed of crystalline Yb 2 Si 2 O 7 with a small amount of Yb 2 SiO 5 and amorphous Yb 2 Si 2 O 7 . It had a dense structure containing pores, microcracks, and other types of defects. TG-DTA tests showed that there was almost no mass change from room temperature to 1200 °C, although a sharp exothermic peak appeared at 1038 °C, indicating that the amorphous phase had crystallized. The thermal conductivity of the coating decreased with increasing temperature, reaching a minimum of 0.68 W/(m·K) at 600 °C, followed by an increase at higher temperatures.

This study investigates the use of cold gas spraying (CGS) for depositing braze filler coatings. In the experiments, pure Cu layers were sprayed onto Mg alloy substrates, which were then joined to AlSi steel by contact reaction brazing in a vacuum furnace. The bonding temperature influenced the dissolution of Cu as well as the eutectic reaction between the coating and substrate. The thickness of the brazed seam was found to be 300 μm although the initial thickness of the Cu layer was just 50 μm. The shear strength of the joint peaked at 37 MPa, corresponding to a brazing temperature of 530 °C. Intermetallic phases and interfacial defects of various types were responsible for the low strength of the joints.

This study investigates the corrosion resistance Gd 2 Zr 2 O 7 /YSZ coatings and a YSZ layer of similar thickness. All coatings were produced by suspension plasma spraying, resulting in a columnar structure. Corrosion tests conducted at 900 °C for 8 h in a molten salt bath show that Gd 2 Zr 2 O 7 is not as corrosion resistant as YSZ. Molten salts react with Gd 2 Zr 2 O 7 producing GdVO 4 along the surface as well as between the columns of the coating. The formation of GdVO 4 between the columns, in combination with the low fracture toughness of Gd 2 Zr 2 O 7 , is likely responsible for the lower corrosion resistance. Furthermore, the presence of another layer of Gd 2 Zr 2 O 7 on top of the Gd 2 Zr 2 O 7 /YSZ coating, to prevent salt infiltration, did not improve corrosion resistance.

Thermal barrier coatings (TBCs) consisting of a MCrAlY bond coat and a YSZ topcoat were air plasma sprayed onto Hastelloy X substrates. Samples were thermally cycled between 100 °C and 1100 °C and thermal fatigue failures were investigated via microstructure analyses. Final fatigue failure was caused by the formation of interface-parallel cracks in the topcoat, which was found to strongly related to the oxidation behavior of the bond coat. The development of oxide layers was therefore studied in detail and a thermo-kinetic model was used to explore the role of elemental diffusion in oxide formation.

In this work, steel columns are metallurgical bonded to tempered glass with the aid of atmospheric plasma spraying and low-temperature soldering. Glass surfaces were sandblasted using different grain sizes, then multilayer (Al 2 O 3 -Cu) coatings were applied at various power levels and spraying distances. Sn-Ag-Cu solder paste was then painted on the metallized glass and steel structures were set in place and soldered in a reflow oven. The interfacial bond strength of the alumina layer was measured along with the strength of the solder joint. The results are presented and correlated with sandblasting grain size and spraying heat input.

ZnO nanostructured coatings have been prepared on Al 2 O 3 substrates fitted with Au electrodes on one side and a Pt heater on the other, forming a solid-state gas sensor. The coatings were deposited by solution precursor plasma spraying (SPPS) using aqueous zinc acetate as the precursor solution. FE-SEM images show that the coatings are nanostructured with grain sizes of 50-100 nm. Surface morphology and grain size were found to be influenced by the flow rate of H 2 in the plasma forming gas. The gas sensing function was characterized by measuring the electrical resistance of the coating in the presence of NO 2 gas, showing good sensitivity down to the sub-ppm range.

The aim of the study presented in this paper was to develop the next generation of production ready air plasma sprayed thermal barrier coating with a low conductivity and long lifetime. In order to achieve these goals; a number of coating architectures were produced using commercially available plasma spray guns. Modifications were made to powder chemistry including; high purity powders for sintering resistance, Dysprosia stabilised Zirconia powders and powders containing porosity formers. Agglomerated & Sintered (A&S) and Hollow Oven Spherical Powder (HOSP) morphologies were used to attain beneficial microstructures. Finally, dual layer coatings were produced using the different powder morphologies. Evaluation of the thermal conductivity of the coating systems from room temperature to 1200°C was conducted using laser flash technique. Tests were done on as-sprayed samples and samples heat treated for 100 hours at 1150°C in order to evaluate the first stage sintering resistance of the coating systems. Thermal conductivity results were correlated to coating microstructure using image analysis of porosity and crack content. The results show the influence of beneficial porosity on reducing the thermal conductivity of the produced coatings.

Yttria-stabilized zirconia coatings were deposited onto a Ti-6Al-4V substrate through a microplasma spray technique and incubated in simulated body fluid (SBF) for different periods of time (3, 7, 14, 28 days). The formation of apatite on the surface was investigated to evaluate the bioactivity of the coatings. Surface morphologies and structural changes in the coatings before and after immersion were analyzed by optical microscopy, scanning electron microscopy, and x-ray diffractometry. The calcium (Ca 2+ ) concentration in the solutions was measured directly after the samples were removed, using an inductively coupled plasma atomic emission spectrometer (ICP). The results showed that yttria-stabilized zirconia coatings can be produced by microplasma spraying and, even though the coatings contain few small unmelted particles, apatite can be formed on the coatings that are soaked in SBF solution. These results indicate that the yttria-stabilized zirconia coatings exhibited definite bioactivity.

The flattening behavior of individual splats plays a fundamental role in the elaboration of thermal spray coatings. In the PROTAL process, an in-situ laser treatment is coupled with spraying operations. It was shown that a pulsed laser irradiation can effectively suppress the splashing phenomenon of splats. This aspect was primarily attributed to the efficient removal of surface adsorbates/condensates. But, it may also be enhanced by the modification of the surface topography that improves the surface wettability. Therefore, this study deals with the effects of the surface microroughness modifications on the surface wettability induced by the PROTAL process. Several roughness parameters characterizing the surface topography are also discussed from a static wettability point of view.

The aim of this work was to study the modifications induced by 10 ns single or cumulative pulses of a Q-switched Nd:YAG laser emitting in the near-infrared (λ = 1064 nm) on a pure aluminum surface with a laser energy density leading to a regime of interaction below the material ablation. The influence of these laser substrate pre-treatments on the mechanical behavior of an 83 µm thick alumina plasma sprayed coating was observed by evaluating the integrity of the coating/substrate interface with a "laser-ultrasonic method" thanks to a special set up using a probe laser interferometer. An increase in the alumina coating adhesion considering cumulative pulses for a laser energy density of 0.7 J/cm 2 was observed above 100 laser pulses. The highest adhesion was obtained for a laser treatment considering 1000 shots. For a single pulse laser treatment, this increase was found applying an energy density of 1.8 J/cm 2 . These results were correlated with the observation of modifications on topography and morphology of the aluminum surface after laser irradiations using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results showed that the improvement of the adhesion of the plasma-sprayed alumina coatings was correlated to changes of the aluminum oxide morphology.

Thermal Spray Toolkit is a developing toolkit for thermal spray applications based on RobotStudio™ software which is developed by Asea Brown Bovrie Ltd (ABB). This toolkit is composed of several functional modules including PathKit, ProfileKit and MonitorKit. PathKit provides numerous methods to create trajectory on different surfaces including square and rectangular surfaces, round surfaces, curved surfaces and rotating workpieces. ProfileKit permits coating surface analysis by importing a surface profile and it can also guide users to select the right spray parameters according to specific materials. MonitorKit can capture the robot displacement in real-time during the spray process. Thermal Spray Toolkit is a toolkit developed to apply robotics in thermal spray applications whose reliability has been confirmed by the experimental results.